The homopolymerization of tetrafluoroethylene and the copolymerization of tetrafluoroethylene and ethylenically unsaturated comonomers in aqueous medium can be carried out by two distinctly different procedures. In one procedure, little or no dispersing agent is employed and agitation is carried out vigorously in order to produce a precipitated resin, commonly referred to as "granular" resin. In the other procedure, sufficient dispersing agent is employed and agitation is mild in order to produce small colloidal size particles dispersed in the aqueous reaction medium. In this second procedure, called aqueous dispersion polymerization, precipitation (i.e., coagulation) of the resin particles is avoided. The two procedures produce distinctly different products. The granular product can be molded in various forms, whereas the resin produced by the aqueous dispersion method cannot be molded but is fabricated by dispersion coating or by converting to powder for paste extrusion with a lubricating medium. In contrast, the granular resin is incapable of being paste extruded or dispersion coated.
A disadvantage which occurs during aqueous dispersion polymerization is the formulation of coagulum, i.e., unwieldy large clumps of resin particles, which settle out of the polymerization medium and may clog the equipment as well as reduce the yield of suspended, colloidal size resin particles. This coagulum formation is particularly evident when ionic polymerization initiators are employed. Several methods have been developed in the art to reduce the amount of coagulum formed. For example, Bankoff U.S. Pat. No. 2,612,484 teaches that selected hydrocarbon waxes can be added to the polymerization medium to stabilize the colloidal size resin particles produced and thereby prevent their premature coagulation. In addition, Punderson U.S. Pat. No. 3,391,099 teaches that if addition of dispersing agent to the reaction medium is programmed (i.e., added in increments), the nucleation of resin particles may be controlled so as to reduce formation of coagulum.
Despite the teachings of the art to reduce coagulum formation, further reduction of coagulum formation is desirable.